1. Technical Field
This invention relates to switching devices and, more particularly, to techniques for switching a multiplicity of data signals in communication networks.
2. Discussion
Computer architectures now commonly include a large number of processors that execute programs concurrently. These so called parallel computing architectures typically require a communication network that allows efficient data transfer between processors, and between an individual processor and its associated memories. In many parallel processing systems it is desirable to permit many processors to transfer information simultaneously. The use of optics to accomplish this task is particularly effective since optical systems can provide appropriate inherent parallelism, suitable band widths and low interaction between the separate beams in a linear medium. One of the most important optical systems is known as a crossbar network. A crossbar network permits a plurality of processors or memories to be dynamically interconnected in any selected configuration without moving any existing interconnections.
FIG. 1 illustrates a known "star" crossbar network 10 that is disclosed in more detail in the paper authored by MacDonald et al., in Electron Lett. 14 (1978) page 502, entitled "Optoelectronic Broadband Switch Array" which is hereby incorporated by reference. Briefly, network 10 includes four transmitters 12, 14, 16 and 18 which may be connected to one or more processors. The transmitters provide input signals which are coupled to optical fibers 20, 22, 24 and 26. The fibers are, in turn, fanned out and made incident on a plurality of detectors 28. Each of the detectors includes a photodetector 29 connected in series with a preamplifier 31. Each of the detectors operates to selectively convert light incident on its associated photodetector to an appropriate electrical signal. The detectors are arranged in an array of rows and columns. Each of the detectors in a row are connected to a common output line 33. The outputs of the lines 33 are coupled for rebroadcast to suitable output receivers labeled 30-36 in FIG. 1. Typically, optical fibers are used to transmit the signals from the crossbar network 10 to these receivers. Accordingly, an additional reconversion of the electrical signals on lines 33 to optical signals are performed by optical repeaters 38-44.
Typically, the selection of which detector to supply its output signal onto line 33 is made by bias control circuitry (not shown). In many of the known crossbar networks it is necessary to provide a deactivating bias to all of the detectors which are not selected. As a result, the switching control is somewhat complicated and unwanted noise crosstalk between detectors has been experienced. In addition, each detector requires its own preamplifier circuitry. Thus, the necessity for these additional components limits the ability to fabricate large, compact crossbar networks.